• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.543-550
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• 2010

This paper investigated the synthesis conditions of nano-sized $TiO_2$ powder in a hydrothermal process at a temperature range of $100{\sim}180^{\circ}C$ considering the precipitation agent, precipitation pH, reaction temperature and time. Titanium hydroxide formed by $NH_4OH$ exhibited a lower crystallization temperature than that by NaOH and formed less aggregated $TiO_2$ particles. As the precipitation pH increased above 8, the shape of the particles changed from spherical to needle form, which appeared to be caused by dissolution and re-precipitation of the titanium hydroxide in an alkali environment.

• Journal of the Korean institute of surface engineering
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• v.41 no.2
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• pp.69-75
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• 2008

Electrochemical behaviors of surface modified and MC3T3-E1 cell cultured Ti-30Ta alloys have been investigated using various electrochemical methods. The Ti alloys containing Ta were melted by using a vacuum furnace and then homogenized for 6 hrs at $1000^{\circ}C$. MC3T3-E1 cell culture was performed with MC3T3-E1 mouse osteoblasts for 2 days. The microstructures and corrosion resistance were measured using FE-SEM, XRD, EIS and potentiodynamic test in artificial saliva solution at $36.5{\pm}1^{\circ}C$. Ti-Ta alloy showed the martensite structure of ${\alpha}+{\beta}$ phase and micro-structure was changed from lamellar structure to needle-like structure as Ta content increased. Corrosion resistance increased as Ta content increased. Corrosion resistance of cell cultured Ti-Ta alloy increased predominantly in compared with non cell cultured Ti- Ta alloy due to inhibition of the dissolution of metal ion by covered cell. $R_p$ value of MC3T3-E1 cell cultured Ti-40 Ta alloy showed $1.60{\times}10^6{\Omega}cm^2$ which was higher than those of other Ti alloy. Polarization resistance of cell-cultured Ti-Ta alloy increased in compared with non-cell cultured Ti alloy.

• Journal of the Korean institute of surface engineering
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• v.41 no.2
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• pp.57-62
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• 2008

Electrochemical properties of Ti-30Ta-$(3{\sim}15)$Nb alloys coated by HA/Ti compound layer have been studied by various electrochemical method. Ti-30Ta binary alloys contained 3, 7, 10, and 15 wt% Nb contents were manufactured by the vacuum furnace system. The specimens were homogenized for 24 hrs at $1000^{\circ}C$. The samples were cut and polished for corrosion test and coating. It was coated with HA/Ti compound layer by magnetron sputter. The HA/Ti non-coated and coated morphology of Ti alloy were analyzed by x-ray diffractometer(XRD) and filed emission scanning electron microscope(FE-SEM). The corrosion behaviors were investigated using potentiodynamic method in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The homoginazed Ti-30Ta-$(3{\sim}15wt%$)Nb alloys showed the ${\alpha}+{\beta}$ phase, and ${\beta}$ phase peak was predominantly appeared with increasing Nb content. The microstructure of Ti alloy was transformed from needle-like structure to equiaxed structure as Nb content increased. HA/Ti composite surface showed uniform coating layer with 750 nm thickness. The corrosion resistance of HA/Ti composite coated Ti-alloys were higher than those of the non-coated samples in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Especially, corrosion resistance of Ti-Ta-Nb system increased as Nb content increased.

• Journal of the Korean institute of surface engineering
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• v.42 no.4
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• pp.161-168
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• 2009

Effects of TiN/Ti multilayer coating on the Ti-30Ta-xZr alloy surface were studied by using various experiments. The Ti-30Ta containing Zr (5, 10 and 15 wt%) were melted 10 times to improve chemical homogeneity by using a vacuum furnace. And then samples were homogenized for 24 hrs at $1000^{\circ}C$. The specimens were prepared for TiN/Ti coating by cutting and polishing. The prepared specimens were coated with TiN/Ti multilayers by using DC magnetron sputtering method. The analyses of coated surface and coated layer were carried out by field emission scanning electron microscope(FE-SEM), EDX, and X-ray diffractometer(XRD). From the microstructure and XRD analysis of Ti-30Ta-xZr alloys, The equiaxed structure was changed to needle-like structure with increasing Zr content. And $\alpha$-peak and elastic modulus increased as Zr content increased. The $\alpha$ and $\beta$ phase predominantly were found in the specimen containing high Zr content. According to the analysis of TiN/Ti coating layer, the surface defects and structures of Ti-30Ta-xZr were covered with TiN/Ti coating layer and surface roughness decreased.

• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.691-699
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• 2008

Electrochemical characteristics of Ti-30Ta-xZr alloys coated with HA/TiN by using magnetron sputtering method were studied. The Ti-30Ta containing Zr(3, 7, 10 and 15wt%) were 10 times melted to improve chemical homogeneity by using a vacuum furnace and then homogenized for 24hrs at $1000^{\circ}C$. The specimens were cut and polished for corrosion test and coating, and then coated with HA/TiN, respectively, by using DC and RF-magnetron sputtering method. The analyses of coated surface and coated layer were carried out by using optical microscope(OM), field emission scanning electron microscope(FE-SEM) and X-ray diffractometer(XRD). The electrochemical characteristics were examined using potentiodynamic (-1,500 mV~ + 2,000 mV) and A.C. impedance spectroscopy(100 kHz ~ 10 mHz) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The microstructure of homogenized Ti-30Ta-xZr alloys showed needle-like structure. In case of homogenized Ti-30Ta-xZr alloys, a-peak was increased with increasing Zr content. The thickness of TiN and HA coated layer showed 400 nm and 100 nm, respectively. The corrosion resistance of HA/TiN-coated Ti-30Ta-xZr alloys were higher than that of the non-coated Ti-30TaxZr alloys, whic hindicate better protective effect. The polarization resistance($R_p$) value of HA/TiN coated Ti-30Ta-xZr alloys showed $8.40{\times}10^5{\Omega}cm^2$ which was higher than that of non-coated Ti-30Ta-xZr alloys.

• Journal of the Korean institute of surface engineering
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• v.41 no.5
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• pp.181-188
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• 2008

A.C. impedance properties of HA/Ti compound layer coated Ti-30Ta-($3{\sim}15$)Nb alloys have been studied by electrochemical method. Ti-30Ta binary alloys contained 3, 7, 10 and 15 wt% Nb were manufactured by the vacuum furnace system. And then specimen was homogenized at $1000^{\circ}C$ for 24 hrs. The sample was cut and polished for corrosion test and coating. It was coated with HA/Ti compound layer by magnetron sputter. The non-coated and coated morphology of Ti alloy were analyzed by X-ray diffractometer (XRD), energy X-ray dispersive spectroscopy (EDX) and filed emission scanning electron microscope (FE-SEM). The corrosion behaviors were investigated using A.C. impedance test (PARSTAT 2273, USA) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Ti-30Ta-($3{\sim}15\;wt%$)Nb alloys showed the ${\alpha}+{\beta}$ phase, and $\beta$ phase peak was predominantly appeared in the case of increasingly Nb contents. The microstructures of Ti alloy were transformed from needle-like structure to equiaxed structure as Nb content increased. From the analysis of coating surface, HA/Ti composite surface uniformed coating layer with 750 nm thickness. The growth directions of film were (211), (112), (300) and (202) for HA/Ti composite coating on the surface after heat treatment at $550^{\circ}C$, whereas, the growth direction of film was (110) for Ti coating. The polarization resistance ($R_p$) of HA/Ti composite coated Ti-alloys were higher than those of the Ti and HA coated samples in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Especially, corrosion resistance of Ti-Ta-Nb system increased as Nb content increased.

• Transactions on Electrical and Electronic Materials
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• v.13 no.2
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• pp.85-88
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• 2012

Studies on the effects of layered silicate content on the AC electrical treeing and breakdown behaviors of epoxy/layered silicate nanocomposites were carried out in needle-plate electrode geometry. Wide-angle X-ray diffraction (WAXD) analysis and transmission electron microscopy (TEM) observation showed that 1 wt% of the multilayered silicate was fully exfoliated into nano-sized monolayers in the epoxy matrix however, over 3 wt% of the silicate was in an intercalated state. When 1 wt% layered silicates were incorporated, an electrical tree was initiated in 439 min and propagated at a speed of 2.3 ${\mu}m$/min after applying 781.4 kV/mm, representing a decreased in starting initiation time by a factor of 11.0 and increase in propagation speed by a factor 8.2 in comparison with neat epoxy resin. These values were in great decline after the layered silicate content was increased to 3wt% which implies that the exfoliated silicate blocked the tree initiation and propagation processes effectively. However the effect was largely decreased in the intercalated state.

• Korean Journal of Crystallography
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• v.17 no.1
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• pp.14-18
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• 2006

MOCVD 공정방법에 의해 수직정렬된 ZnO 나노선을 합성하고 공정조건 제어에 의해 합성되는 나노선의 물리적, 광학적 특성이 어떻게 변화하는지를 고찰하고자 하였다. 온도 및 산소분압제어 등의 공전변수 제어를 통하여 ZnO 나노 구조체는 나노선, 나노로드 뿐만 아니라 나노바늘 (nano-needle) 등 다양한 구조로 변화되었으며 그 직경 및 길이도 제어가 가능하였다. 전체적으로 양호한 특성의 wurzite 구조를 나타내었으며 기판에 수직인 방향으로 [0001] 방향으로 성장하였다. 광학특성에서는 나노선 직경이 작아질수록 주방출 피크의 천이현상이 관찰되었다.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.267-272
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• 2008

The purpose of this study is to improve the environmental applicability of nonwovens by using special composition. Polypropylene spunbonded and needle punched nonwovens which have the lower cost than polyester nonwovens were used as the raw materials to manufacture the natural fiber used nonwoven geotextiles. These geotextiles were made by use of the thermal bonding methods and composed of jute(or flax)/polypropylene staple fiber blends were obtained in consideration of environmental application. Finally, the engineering properties of natural fiber used nonwoven geotextiles were investigated as eco-friendly materials.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.97-97
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• 2013

The exterior structures of natural organisms have continuously evolved by controlling wettability, such as the Namib Desert beetle, whose back has hydrophilic/hydrophobic contrast for water harvesting by mist condensation in dry desert environments, and some plant leaves that have hierarchical micro/nanostructures to collect or repel liquid water. In this work, we have provided a method for wettability contrast on metals by both nano-flake or needle patterns and tuning of the surface energy. Metals including steel alloys and aluminum were provided with hierarchical micro/nanostructures of metaloxides induced by fluorination and a subsequent catalytic reaction of fluorine ions on metal surfaces in water with various ranges from room to boiling temperature of water. Then, a hydrophobic material was deposited on the structured surfaces, rendering superhydrophobicity. Plasma oxidization induces the formation of superhydrophilic surfaces on selective regions surrounded by superhydrophobic surfaces. We show that wettability contrast surfaces align liquid water within patterned hydrophilic regions during the condensation process. Furthermore, this method could have a greater potential to align other liquids or living cells.